(1) Field of the Invention
This invention relates to a regenerated cellulose hollow fiber used as a permeable membrane for dialysis and ultrafiltration and to a process for producing the same.
(2) Description of the Prior Art
In recent years regenerated cellulose hollow fibers have been popularly used as dialysis membrane such as a blood dialyzer, i.e., an artificial kidney. The following properties are desired for regenerated cellulose hollow fibers: (1) balanced water permeability and dialysis performances, (2) perfectly circular hollow cross-section, (3) feedom from pinholes and other imperfections, (4) enhanced wet strength and dimensional stability, and (5) no toxicity hazard. Regenerated cellulose hollow fibers possessing all of such desired properties are not yet known.
U.S. Pat. No. 3,888,771 discloses a regenerated cellulose hollow fiber produced from a cuprammonium cellulose solution. This regenerated cellulose hollow fiber is commercially available but not completely satisfactory in the handling characteristics. This is because its degree of crystallite orientation and wet strength/wet elongation ratio are as low as only approximately 75% and approximately 1.1 g/d, respectively. Furthermore, the regenerated cellulose hollow fiber is not always sanitarily safe because it is possible that a trace amount of copper remains in the wall thickness of the hollow fiber.
U.S. Pat. No. 3,546,209 discloses a process for preparing a regenerated cellulose hollow fiber from a cellulose ester wherein the cellulose ester combined with a plasticizer is melt extruded into a cellulose ester hollow fiber which is then hydrolyzed into a regenerated cellulose hollow fiber. The regenerated cellulose hollow fiber prepared by this process is not completely satisfactory in its handling characteristics because the hollow fiber possesses a low wet strength and, when it is reinstated from a dry state to a wet state, exhibits a large elongation. Furthermore, the regenerated cellulose hollow fiber is liable to be distorted from its circular cross-section in the melt extruding and hydrolyzing steps.